1. Field of the Invention
This invention relates to a process for the filtration of liquors containing organic solvents used in dry cleaning. The invention also relates to filtration aids used in the filtration of these liquors.
2. Description of Related Art
In dry cleaning, soil is detached from fabrics and leather goods by cleaning liquors predominantly containing organic solvents. To enable the solvents to be reused, the various soils detached, which are either dispersed or dissolved in the organic solvents, have to be completely removed from the solvents without the composition of the cleaning liquors being significantly affected.
In corresponding processes for treating solvents used in dry cleaning, all filterable, i.e. undissolved, impurities have to be removed from the solvent in a first step. This is normally done in filters charged with kieselguhr. In kieselguhr filters, however, only undissolved soil is filtered off from the cleaning liquors.
If cartridge filters are used for filtering the soiled cleaning liquors, the filtration result is much better. Typically, the cartridges of such filters contain active carbon or mixtures of active carbon and activated alumina, e.g., bentonite. Materials such as these not only have a very large surface area, they also show a good adsorption effect with respect to dissolved soil. Accordingly, the cleaning liquors filtered through these materials are much cleaner than those filtered through kieselguhr, so that subsequent distillation of the cleaning liquors can be carried out at longer intervals. Cartridge filters of the type in question are described, for example, in current FCR-Information No. 174 of the Forschungsstelle Chemischreinigung, published in July, 1977.
Unfortunately, the surfactant content of certain cleaning liquors causes problems in adsorption filters of the type in question. Surfactants emanating, for example, from prespotting are inadequately adsorbed. This results in an accumulation of prespotting agents and cleaning boosters in the cleaning liquors. So-called "rings" on thin fabrics, such as, for example, on linings or lightweight outer clothing, are the direct result (cf. WRP, No. 6/1982, pages 8 et seq.).
Distinct improvements in the kieselguhr filters described above are provided by the filters disclosed in DE-OS No. 30 07 633 which consist completely or partly of finely-divided, water insoluble, alkali metal alumino-silicates, i.e., zeolites. In some cases, these zeolite filters are used in combination with kieselguhr filters and, above all, enable even dissolved acid traces to be removed from the cleaning liquors. However, distillation of the solvent mixtures is unavoidable on account of the numerous dissolved soils.
The object of the present invention is mainly to free the solvents or solvent mixtures used in dry cleaning from dissolved soil, odorous substances and dyes, prespotting agents and cleaning boosters so that by improved filtration, distillation of the solvents is only necessary at prolonged intervals.